Possivelmente A Casa Distante, um filme de TV australiano 1992.
A partir de IMDb:
Jim and Maria Harrison are an ordinary couple living in an ordinary suburb. The only extraordinary thing about them is that their daughter Sally is about to become ruler of the galaxy.
The Harrisons were expecting their first child. On the way to the hospital the weather was strange, the electrical system of the family sedan failed, and when their child is born, it was unexpectedly twins, a boy and a girl, Bobby and Sally.
What the Harrisons did not know was that the leader of the Galazy Empire was also pregnant at the time. As there was a war between the Empire and the Confederacy, to safeguard the Empires child, it was implanted in Maria's womb and left up to her to raise.
Twelve years pass and the twins have grown up, but the time has come for Sally to return to her real family, and rule as she was meant to. Unfortunately she is knocked over by a car while riding her new bike and is taken to hospital where it is discovered that she is an alien. With the government involved, Sally is unable to return to either family until the Harrisons make plans to rescue her and return her to her real mother and fulfill her destiny out among the stars.
O filme está no YouTube (em espanhol castelhano).
Encontrado pesquisando neste site por princesa alienígena [identificação-história] que retornou, entre outros, Identificação: Programa de TV de ficção científica para jovens adultos 90 / 80s. Jovem acaba por ser uma princesa alienígena (ou algo assim)